[Issue 17652] New: [DIP1000] opApply allow to escape reference to scope variable

[via Digitalmars-d-bugs]

https://issues.dlang.org/show_bug.cgi?id=17652

          Issue ID: 17652
           Summary: [DIP1000]  opApply allow to escape reference to scope
                    variable
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Keywords: safe
          Severity: normal
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: mathias.lang at sociomantic.com

```
void main () @safe @nogc
{
    Object o = leak();
    assert(o !is null);
}

Object leak () @safe @nogc
{
    Foo f;
    foreach (object; f)
        if (object !is null)
            return object;
    return null;
}

struct Foo
{
    alias DgType = int delegate (scope Object) @safe @nogc;
    public int opApply (scope DgType dg) @safe @nogc
    {
        scope o = new Object;
        return dg(o);
    }
}
```

The compiler doesn't properly check the type of the delegate it passes to
`opApply`, allowing to pass a delegate which needs a non-scope parameter.

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